1. Field of the Invention
The invention concerns a device to detect thermal radiation with at least one shielded thermal detector element to transduce the thermal radiation into an electrical signal. In addition to the device a use of the device is specified.
2. Description of the Prior Art
A conventional device 300 for detection of thermal radiation is shown in FIG. 7. The device 300 has a substrate 310 and a sensor 320 that is attached to the substrate 310 by means of a casting compound 312. The device 300 also has a protective housing 330 that is arranged over the sensor 320 and attached to the substrate 310 by means of a hermetically sealed bonding connection 333. The protective housing 330 is dimensioned such that said protective housing 330 does not directly contact the sensor 320, such that an inner space 335 is fashioned between the sensor 320 and the protective housing 330. The protective housing 330 has a top side 332 that is arranged facing away from the sensor 320. A window opening 334 is provided in the top side 332, which window opening 334 is arranged above the sensor 320 so that light from outside the protective housing 330 can strike the sensor 320. A glass window 331 is placed hermetically sealed into the opening 334.
The protective housing 330 is made of metal, such that the sensor 320 is electromagnetically shielded from the protective housing 330. The glass window 331 is also inserted gas-tight into the window opening 334 and the bonding connection 333 is fashioned gas-tight, such that the inner space 335 is evacuated or charged with inert gas or, respectively, hydrogen. The sensor 320 is thereby protected from atmospheric influences. However, it is disadvantageous that the device 300 has a large space requirement due to the large structural height of the protective housing 330. Both the insertion and sealing of the glass window 331 in the window opening 334 and the fashioning of the hermetically sealed bonding connection 333 in the manufacture of the device 300 are also complicated and cost-intensive.
A device for detection of thermal radiation is described in DE 100 04 216 A1, for example. This device is designated as a pyrodetector. The detector element is a pyroelectric detector element. It has a layer structure with two electrode layers and a pyroelectric layer with pyroelectrically sensitive material arranged between the electrode layers. This material is lead zirconate titanate (PZT). For example, the electrodes consist of platinum or of a chromium-nickel alloy absorbing the thermal radiation. The thermal detector element is connected with a detector substrate made of silicon (silicon wafer). An insulation layer for electrical and thermal insulation of the detector element and the detector substrate from one another is arranged between said detector element and said detector substrate. The insulation layer has an evacuated cavity that extends across a base surface of the detector element, a support layer of the cavity and a cover of the support layer and the cavity. The support layer consists of polysilicon. The cover is made of a boron-phosphorus silicate glass (BPSG). A readout circuit is integrated into the detector substrate to read out, process and/or relay the electrical signal generated by the detector element. The readout circuit is realized via the CMOS (Complementary Metal Oxide Semiconductor) technique.
A device for detection of thermal radiation that is comparable to this is known from DE 195 25 071 A1. The thermal detector element is likewise a pyroelectric detector element as described above. The detector element is arranged on a multilayer detector substrate. The detector element is attached to a silicon layer of the detector substrate via one of its electrode layers. The silicon layer is located on an electrically insulating membrane of the detector substrate. For example, the membrane consists of Si3N4/SiO2/Si3N4 triple layer. The membrane is in turn applied on a silicon substrate of the detector substrate. The silicon substrate has an exposure window (detection window) with a base surface that essentially corresponds to a base surface of the pyroelectric detector element. The exposure window is a cutout of the silicon substrate. Substrate material (silicon) of the substrate is thereby removed up to the membrane. The thermal radiation arrives at the detector element through the exposure window and there leads to an evaluable electrical signal. For this purpose, the membrane is characterized by a suitable transmission for the thermal radiation. A readout circuit for the electrical signal is integrated into the silicon layer, laterally offset from the detector element. The detector substrate also acts as a circuit substrate of the readout circuit.
In the known devices a number of detector elements can be present (detector element array). The electrical signal of each of the detector elements is thereby to be read out separately. For this the electrode layers of each of the detector elements are typically electrically contacted via bonding wires. However, this entails a significant space requirement for a wiring of the detector elements, with the result of a limited, relatively low detector element density (number of detector elements per surface segment of the detector substrate).